A technology for identifying motor constants in a vector control method for a permanent magnet synchronous motor is disclosed in Japanese Patent Laid-Open No. 2001-145399. In the technology in said Patent Document, d-axis and q-axis voltages are detected by a detector attached to an electric power converter, and motor constants are identified by three processes described below.
(1) An induced voltage coefficient of the motor is identified from a difference between a voltage command value and the detected voltage value for the q-axis (torque) component in vector control.
(2) A motor resistance value is identified from a difference between a voltage command value and the detected voltage value for the d-axis (magnetic flux) component in vector control.
(3) If the motor resistance value identified in (2) above exceeds a limit value, a switchover occurs to an operation for identifying a q-axis inductance from the voltage difference of the d-axis component.